The problem of quantizing gravitation dates back to the middle parts of the twentieth century. Richard Feynman in [1]} introduced the path integral formalism to the problem of gravitation in order to start a journey towards quantization of gravity. In a perturbative manner, he was able to write down the Feynman rules for graviton sources and gravitons. In all fairness he ushered in the era of effective field theoretical formalisms that have been applied to general relativity (GR) and other extended theories of gravitation, for example recently in [2]}.
